Melt the butter in a medium pan over medium high heat till fully melted. Remove from heat and whisk in the sugar and cocoa powder. Mix in the salt, vanilla, and eggs until well mixed, then mix in the flour. Set aside the pan.
Preheat the oven to 175c (350f)
Cream together the butter and sugars with a hand mixer until fluffy. Add in the eggs and vanilla and mix well. Mix in the salt, baking soda, baking powder and flour, and mix well. Fold in the chocolate chips.
Line the bottom of a 9x9 plan with one strip of parchment, that goes up two sides of the pan.
Spread the cookie dough evening across the pan, making sure to push it into the corners.
Lay down one layer of 16 oreos evenly on top of the cookie dough.
Pour the brownie batter on top of the oreos, and smooth it into the corners with a spatula.
Bake for 30-35 minutes. Cool on a wire rack, ideally overnight allowing the flavors to meld together and the brownies to fully solidify.
Cut around the edges with a knife, lift the brownies out of the pan, and cut in squares.
